Nematodes are blamed for causing the greatest damages to agriculture in tropical, subtropical and temperate regions worldwide (Nickle W. R. (Editor). 1991. Manual of Agricultural Nematology, Marcel Dekker, Inc., New York, N.Y. Pub. 1035 pp). Plantain alone has about 20% nematode-related losses of world production, representing $178 millions each year (Sasser J. N. and Freckman D. W. 1987. A world perspective on nematology: the role of the society. Vistas on nematology: a commemoration of the twenty-fifth anniversary of the Society of Nematologists/edited by Joseph A. Veech and Donald W. Dickson. p. 7-14). Plantain and banana plantations are significantly affected by Radopholus similis. 
Meloidogyne spp is the most important plant parasitic nematode, for its activity causes losses between 11% and 25% of crops in almost all the tropical regions (Sasser J. N. 1979. Root-knot nematodes. Ed. F. Lamberti & C. E. Taylor, Academic Press, London, p 359). Consequently, there is a great need to control those parasites that were fought against with chemical nematicides in the past. Such compounds can be highly effective; however, many of them pose a great danger on the environment. In some cases the regulating authorities have limited the amount or frequency, or both in the use of such compounds, thus compromising their nematicidal effectiveness.
Nematode control still falls short. The use of chemical nematicides is restricted each day more and more, because they have highly toxic and widespread action compounds. As a result, efforts have been made to identify the effective means to eliminate the damage caused by nematodes, in favor of reducing the use of chemical pesticides. One of the approaches is the use, of biological ones with specific mode of actions and relatively safer toxicological profiles, instead of chemical nematicides. Some of the alternative nematicides include ABG-9008, a Myrothecium verrucaria fungus metabolite and a combination of avermectines (or related compounds, like milbecines) with fatty acids (Abercrombie K. D. 1994. Synergistic pesticidal compositions. U.S. Pat. No. 5,346,698. Mycogen Corporation. September. 13). Likewise, a method that includes concurrent administration to eliminate damages caused to plants by nematodes, the site, soil or seeds that need treatment of a) a Myrothecium verrucaria fungus metabolite and b) a chemical pesticide, as well as the synergistic nematicide compositions useful in this case, is claimed under patent (Warrior P., Heiman D. F. and Rehberger Linda A. 1996. Synergistic nematocidal compositions. Abbott laboratories. WO9634529, 1996 Nov. 7). Another approach is to combine spores of Pasteuria penetrans a nematode bacterial parasite, with organophosphorated nematicides (Nordmeyer D. 1987. Synergistic nematocidal compositions of Pasteuria penetrans spores and an organophosphorus nematocide. 1987. CIBA-GEIGY AG Patent AU 06057386A1. Jan. 29, 1987).
However, preparation of P. penetrans spores at industrial scale faces the problem that the organism is an obligated parasite; hence it must be grown in in situ nematodes, isolated from nematode infested root digests.
Chitinolytic fungi and bacteria that share the nematode's habitat, may have certain biological balance and somehow restrict nematode proliferation. Two strains of chitinolytic bacteria (Toda T. and Matsuda H. 1993. Antibacterial, anti-nematode and/or plant-cell activating composition, and chitinolytic microorganisms for producing the same. Toda Biosystem Laboratory, Japan. U.S. Pat. No. 5,208,159, May 4, 1993) have been claimed as antibacterial, antinematode and/or plant-cell activating composition.
There are some examples of the chitinolytic effect on nematodes. Some of the most significant are the strains of new bacteria described (Suslow T. and Jones D. G. 1994. Novel chitinase-producing bacteria and plants. DNA Plant Technology Corporation, U.S. Pat. No. 4,940,840, Jul. 10, 1990) that are created by the introduction of DNA that codifies for chitinase production, an enzyme that can degrade chitin in fungi and nematodes. The strains are useful in the production of chitinase to inhibit plant pathogens. Novel plants resistant to pathogens are described too, as the result of introduction of DNA codifying for chitinase production.
Other instances of microorganisms that reduce nematode populations that attack plants in natural conditions are described.
Rodriguez-Kabana et al. (Rodriguez-Kabana R., Jordan J. W., Hollis J. P. 1965. Nematodes: Biological control in rice fields-role of hydrogen sulfide. Science. 148: 524-26); Hollis and Rodriguez-Kabana (Hollis, J. P., y R. Rodríguez-Kábana. 1966. Rapid kill of nematodes in flooded soil. Phytopathology 56, pp 1015-19) observed correspondence among bacterium Desulfovibrio desulfuricans, hydrogen sulfide production and plant parasitic nematodes, whose population decreased in Louisiana's rice plantations. Sulfides are inhibitors in the electron transport breathing process of the aerobic organism, just like other metabolites produced by certain soil bacteria (Rodríguez-Kábana, R. 1991. Control biológico de nematodos parásitos de plantas. NEMATROPICA, 21(1), pp 111-22).
PAECIL™, also known as BIOACT or Nemachek, is a biological nematicide that contains a patented strain from Paecilomyces lilacinus, in a dry and stable spore concentration for soil and seed treatment. This fungal species is commonly found in all soils worldwide. The patented strain used as PAECIL™ active ingredient has a particular effectiveness against plant parasitic nematodes. It was originally isolated at The Philippines University, and has been developed in Australia, Macquarie University. Furthermore, it has been broadly tested for the control of several kinds of nematodes that attack major crops in Australia, The Philippines, South Africa, and others. PAECIL™ formulation is commercially available as a pesticide registered in The Philippines, under the name of BIOACT®; in South Africa, under the name of PL PLUS; and Indonesia, under the name of PAECIL™. Currently, the Australian National Registration Authority is evaluating the product as a pesticide (Holland, R. PAECIL™. 1998. http://www.ticorp.com.au/article1.htm). The above-mentioned instances fail to solve all parasitic helminth problems. Therefore, the need to implement improved means for parasite control to substitute chemical pesticides and antiparasitic products still remains.
Trematodes cause considerable economic damage to animal production and human health. The diversity of the species, relative benign pathogenicity and endemism in isolated regions seem to be essential factors that effect on the lack of knowledge on trematodes. In general terms, intestinal trematodes are zoonotic and have a large number of reservoir hosts in each species.
Economically speaking, one of the most significant trematodes is Fasciola hepatica, the first known parasitic trematode; it affects man by inhabiting the bile conduits. Its egg is one of the largest, ovoid and operculated from helminthes, and causes digestive malfunction consisting in gastric disepsia, colon motility malfunction, liver and bile vesicle pain, fever and hepatic colic. Other signs may include cystic forms in lungs, eyes, brain, hepatic vein, and other tissues (Saleha A. 1991. Liver fluke disease (fasciolosis) epidemiology, economic impact and public health significance. Southeast Asian J. Trop. Med. Public health 22 supp 1dic. P 361-4)
Zoohelminths have become significant pests to sheep and cattle. Antihelminthic resistance is wide, particularly in populations of small ruminant parasitic nematodes.
New supplementary techniques have been developed, others are under research. Fungus, Duddingtonia flagrans is a predator that forms nets, produce wide wall, motionless spores: clamidospores, able to survive the passage along the intestinal tract of cattle, equines, sheep and swine (Larsen M. 1999. Biological control of helminths. Int J Parasitol. January; 29(1): 139-46, and Larsen, M. 2000. Prospects for controlling animal parasitic nematodes by predacious micro fungi. Parasitology, 120, S120-S121).
Works on D. flagrans in Denmark, France, Australia, USA, and Mexico, have confirmed the strong potential for biological control this fungus has.
Like many other important sheep producing countries, South Africa undergoes a big crisis in terms of antihelminthic resistance, especially in gastrointestinal nematodes in sheep and goat. Significant parasitic helminthes are involved in this phenomenon; however, this causes a particular problem with abomasum hematophage parasite Haemonchus contortus. The studies point out that over 90% of this parasite's strains from the most important sheep producing regions in South Africa, show several drug resistance degrees, in three out of the four antihelminthic groups available in the South African market. Even in areas of common grazing in Northern Province, it was detected in five herds studied in 1993 (van Wyk J. A., Bath G. F. and Malan F. S. 2000. The need for alternative methods to control nematode parasites of ruminant livestock in South Africa. World Animal Review. http://www.fao.org/ag/AGA/AGAP/FRG/FEEDback/War/contents.htm).
Resistance increase has become serious, since it has been experienced in other areas as well. A series of antihelminthic studies have been recently conducted in four Latin American countries: Argentina (Eddi, C., Caracostantogolo, J., Peya, M., Schapiro, J., Marangunich, L., Waller, P. J. & Hansen, J. W. 1996. The prevalence of anthelmintic resistance in nematode parasites of sheep in southern Latin America: Argentina. Vet. Parasitol., 62: 189-197); Brazil (Echevarria F., Borba M. F. S., Pinheiro A. C., Waller P. J. & Hansen J. W. 1996. The prevalence of anthelmintic resistance in nematode parasites of sheep in southern Latin America: Brazil. Vet. Parasitol., 62: 199-206); Paraguay (Maciel S., Giminez A. M., Gaona, C., Waller P. J. & Hansen J. W. 1996. The prevalence of anthelmintic resistance in nematode parasites of sheep in southern Latin America: Paraguay. Vet. Parasitol., 62: 207-212); and Uruguay (Nari A., Salles J., Gil A., Waller P. J. & Hansen J. W. 1996. The prevalence of anthelmintic resistance in nematode parasites of sheep in southern Latin America: Uruguay. Vet. Parasitol., 62: 213-222).
One of the nematodes that causes the greatest damages to cattle is Dictyocaulus viviparous, a parasite that comes to sexual maturity and when adult, is lodged in the lung of cattle, particularly young animals. The diseased caused is known as verminose bronchitis, or bovine Dictyocaulosis, and infestation is produced after ingesting the 3 or infesting larvae, present in the pastures. The treatment requires antihelminthics (Borgsteede F. H. M, de Leeuw W. A. & Burg W. P. J. 1988. A comparison of the efficacy of four different long-acting boluses to prevent infections with Dictyocaulus viviparus in calves. The Veterinary Quarterly, Vol 10, No. 3), but success is at the expense of new strains resistant to the drugs, which make further infested animal treatment harder. The high cost of these products is a restrictive factor to the countries with a large number of resources, and harmful ecological effects are produced with the use of these formulations.
The international problem of anthelmintic resistance is compounded by the fact that, while chemotherapy continues to be the cornerstone of parasite control, there seems little hope that any novel, chemically unrelated anthelmintics will be forthcoming for at least the next decade (Soll, M. D. 1997. The future of anthelmintic therapy from an industry perspective. In J. A. van Wyk & P. C. van Schalkwyk, eds. Managing anthelmintic resistance in endoparasites, p. 1-5. Proceedings of the 16th International Conference of the World Association for the Advancement of Veterinary Parasitology, Sun City, South Africa, 10-15 Aug. 1997).
In the case of bacteria and pathogenic fungi, there are comprehensive reports on biologicals, whose action is mainly based on antagonism and that a large amount of them are commercially available. Some of them are Conquer (Pseudomonas fluorescens that antagonizes Pseudomonas tolassii), Galltrol-A (Agrobacterium radiobacter, that controls Agrobacterium tumefaciens), Bio-Fungus (Trichoderma spp, that controls the following fungi: Phytophthora, Rhizoctonia solani, Pythium spp, Fusarium, Verticillium), Aspire (Candida oleophila I-182 that controls Botrytis spp. and Penicillium spp), etcetera.
One of the most widely active biofungicides is Trichoderma spp (Chet I, Inbar J. 1994 Biological control of fungal pathogens. Appl Biochem Biotechnol; 48(1):37-43) a fungus whose action mechanism is largely discussed, where chitinases that degrade the cellular wall of the host fungus take part. Moreover, there are experimental evidences of chitinolytic action from fungi and bacteria used as fungal disease bioregulators (Herrera-Estrella A, Chet I. 1999. Chitinases in biological control. EXS; 87:171-84). However, this is not the only mode of action of bacteria over phytopathogenic fungi; there are other control ways based on the production of secondary metabolites, like hydrogen cyanide, that manages to inhibit root pathogenic fungi (Blumer C. and Haas D. 2000. Mechanism, regulation, and ecological role of bacterial cyanide biosynthesis. Arch Microbiol March; 173(3):170-7), in the particular case of P. fluorescens CHAO strain.
Analyses of bacterium-bacterium interaction have shown there are three main types: antibiosis, substrate competition and parasitism. In the case of antibiosis, some bacterial strains are known to release antibiotics in order to suppress the surrounding bacterial activity, which may be used for biological control of pathogenic species. Likewise, substrate competition is a mechanism that may as well be used to achieve proper biological control, since the bioregulating organism is able to synthesize siderophores microelement quelant agents, which causes microelement deficiency, mainly iron, in the medium, thus inhibiting the respective pathogenic growth (Ongena M. 1998. Conference on biological controls. Training program in the area of biotechnology applied to agriculture and bioindustry. Gembloux, Belgium).